The present invention relates generally to inspection systems and methods for detecting flaws in continuous web materials, and more particularly, to such systems and methods which employ digital signal processing techniques to detect the flaws.
The inspection of continuous web materials, such as carpet and cloth, and the like, are time consuming, laborious processes. Typically, these operations are performed manually by inspectors who observe the woven or tufted material as it moves past an inspection station. This is a very tedious job, and the quality of the inspection is difficult to control, due to such human factors as eye strain and fatigue.
Consequently, automatic inspection systems have been designed to detect flaws in these materials as they are being produced. For example, a basic system is disclosed in U.S. Pat. No. 3,135,867, entitled "Apparatus for Inspecting a Moving Web." This patent discloses a system which uses a light source to illuminate a moving web and a photomultiplier light detector and mirror arrangement for scanning the moving web. The output of the photomultiplier is thresholded and any signals exceeding the threshold are identified as flaws.
U.S. Pat. No. 4,124,300, entitled "Method for Automatic Fabric: Inspection" discloses a system which employs a laser to irradiate moving web material. Diffraction patterns created by the interaction of the laser light and the material are analyzed to produce data indicative of the quality of the material.
U.S. Pat. No. 4,232,336, entitled "Inspection of Elongated Material" discloses a method of inspecting materials to determine the presence of surface irregularities. A video camera and processing circuitry are employed to analyze light and shadowed areas of the material illuminated with a high intensity strobe light. This invention takes advantage of high-contrast images created by the light/shadow interfaces to provide cues to the presence of flaws.
Although not related directly to the inspection of continuous web material, other inspection systems have been designed which employ image processing techniques to detect flaws of various kinds. For instance, U.S. Pat. No. 4,484,081, entitled "Defect Analysis System" discloses an inspection system employed in inspecting manufactured parts. This system employs a video imaging system and processing circuitry which includes thresholding and region growing circuitry to analyze the defects. The system assumes readily visible high signal-to-noise ratio images. The system analyzes binary images to identify regions of the image whose pixel intensities are above a predetermined threshold. These regions are then analyzed and compared with rejection criteria such as size, shape, direction and position, and the like.
U.S. Pat. No. 3,897,244, entitled "Programmable Image Processor" deals with a system that compares a video image of an object in the field of view to an image of a similar object stored in memory. The system provides an indication of the mismatches between the two images thus indicating misalignment of the subject object relative to orthogonal directions defined in the field of view.
U.S. Pat. No. 4,197,584, entitled "Optical Inspection System for Printing Flaw Detection" discloses a flaw detection system for use with currency printing. The system uses two cameras to scan a reference article and an item under test. The two images are electronically compared and difference signals are generated. A large difference signal is indicative of a flawed test item.
Therefore, although many systems have been designed to inspect continuous web material and other specialized items, all of the systems assume that the flaws to be detected are readily visible, in that the flaws have a high signal-to-noise ratio when viewed by a video camera, or the like.
The signal-to-noise problem in continuous web processing is a serious one due to the fast operating speeds of the machines employed to weave the materials. For example, in a typical production finishing operation for woven cloth, the cloth moves at a rate of eighty to two hundred yards per minute. This requires an extremely fast data processing system to detect and process the video information and output flaw detection data.
In general, the continuous web material, such as cloth and carpet, have a directional nature due to the orthogonal nature of the weaving and tufting process. Accordingly, the flaws that typically exist in the finished products are directional. Heretofore, no continuous web material inspection system has utilized the directional nature of the flaws to detect flaws.
Accordingly, it would be an improvement in the continuous web material inspection art to have an inspection system and method for inspecting moving continuous web material at high speed and provide flaw data for flaws which are normally not easily detected.
It would also be an improvement in the continuous web material inspection art to have an inspection system and method which takes advantage of the directional nature of the defects in the materials in order to detect heretofore undetectable flaws.